title: Cascade reaction of β,γ-unsaturated α-ketoesters with phenols in trityl chloride/TFA system. Highly selective synthesis of 4-aryl-2H-chromenes and their applications.
abstract: The treatment of β,γ-unsaturated α-ketoesters with phenols in the presence of trityl chloride and 4 Å molecular sieves in refluxing trifluoroacetic acid afforded 4-aryl-2H-chromenes in high yields, in which a reverse of the regiochemistry of Jørgensen-Rutjes chromane synthesis was observed. The isolation of 4H-chromene intermediates, confirmed by single-crystal X-ray analysis, indicates that the early stage of the reaction involves a Friedel-Crafts alkylation/cyclodehydration processes. Stirring of the 4H-chromene intermediate with trityl chloride in deuterotrifluoroacetic acid under reflux afforded the 2H-chromene and triphenylmethane in high yields, which implies the late stage of the reaction involves a hydrogen transfer process. Highly selective derivation of the hydroxyl esters to the corresponding hydroxyl amides, amino acids, amino esters and Friedel-Crafts adducts was further accomplished. Our endeavors will lead to a better understanding of the controlling elements behind their structural motifs. The products were confirmed unambiguously from their spectra and by single-crystal X-ray analysis.
authors.affiliation: Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China. ycwu@iccas.ac.cn
authors.forename: Yan-Chao
authors.initials: YC
authors.lastname: Wu
authors.forename: Hui-Jing
authors.initials: HJ
authors.lastname: Li
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.forename: Zhe
authors.initials: Z
authors.lastname: Liu
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.forename: Yong-Jun
authors.initials: YJ
authors.lastname: Chen